April 2011
Volume 52, Issue 14
Free
ARVO Annual Meeting Abstract  |   April 2011
The Roles of RDH8 and RDH12 In The Clearance Of All-Trans Retinal In Rod Photoreceptors
Author Affiliations & Notes
  • Yiannis Koutalos
    Department of Ophthalmology, Medical University of South Carolina, Charleston, South Carolina
  • Chunhe Chen
    Department of Ophthalmology, Medical University of South Carolina, Charleston, South Carolina
  • Debra A. Thompson
    Department of Ophthalmology and Visual Sciences,
    Department of Biological Chemistry,
    University of Michigan School of Medicine, Ann Arbor, Michigan
  • Footnotes
    Commercial Relationships  Yiannis Koutalos, None; Chunhe Chen, None; Debra A. Thompson, None
  • Footnotes
    Support  NIH grant EY014850 (Y.K.), Foundation Fighting Blindness and Research to Prevent BlindnessSenior Scientific Investigator Award (D.A.T.)
Investigative Ophthalmology & Visual Science April 2011, Vol.52, 3648. doi:
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      Yiannis Koutalos, Chunhe Chen, Debra A. Thompson; The Roles of RDH8 and RDH12 In The Clearance Of All-Trans Retinal In Rod Photoreceptors. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3648.

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Abstract

Purpose: : To determine the contributions of retinol dehydrogenases RDH8 and RDH12 to the reduction of all-trans retinal to retinol. All-trans retinal is released in the rod outer segment by photoactivated rhodopsin, and its toxicity is thought to be a contributing factor for several diseases of the retina.

Methods: : Experiments were carried out with single isolated rod photoreceptors from wild-type mice and mice lacking either one or both Rdh8 and Rdh12. All-trans retinal was generated endogenously within the outer segment by bleaching rhodopsin, or was supplied exogenously with bovine serum albumin as carrier. The formation of all-trans retinol was measured by imaging its fluorescence (Ex: 360 nm; Em: >420 nm). The large difference in the absorption spectra of retinal and retinol made it possible to ascertain the contribution of all-trans retinal to the fluorescence signal by using excitation light of different wavelengths (340, 360, and 380 nm).

Results: : The outer segments of rods that lack Rdh8 fail to reduce all-trans retinal to retinol, but those of rods that lack Rdh12 are unaffected. Following exposure to light, the fluorescence of a rod inner segment increases, indicating the influx of all-trans retinal and retinol from the outer segment. The contribution of all-trans retinal to the inner segment retinoid signal is higher in cells that lack either Rdh12 or Rdh8. Rods that lack both Rdh8 and Rdh12 do not show any significant reduction of all-trans retinal to retinol in either the outer or the inner segment. Wild-type cells were effective in reducing moderate loads (5 µM) of exogenous all-trans retinal, but cells that lacked either of the enzymes were not.

Conclusions: : The results are consistent with the localization of Rdh8 and Rdh12 in the rod outer and inner segments, respectively. Rdh8 is responsible for reducing the bulk of the all-trans retinal released by photoactivated rhodopsin in the outer segment. Rdh12 protects the inner segment from a wide spectrum of aldehydes, including any all-trans retinal that has escaped from the outer segment or been released from rhodopsin present in the inner segment. Since the rate of recovery of 11-cis retinal levels after bleaching is not decreased in mice deficient in Rdh8, Rdh12, or both, the reduction of all-trans retinal to retinol in the rod outer segment is not required for the production of fresh 11-cis retinal.Support: NIH grant EY014850 (Y.K.), FFB and RPB Senior Scientific Investigator Award (D.A.T.).

Keywords: photoreceptors • retinoids/retinoid binding proteins • microscopy: light/fluorescence/immunohistochemistry 
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